The use of blow-molding as a method for manufacturing various sorts of articles is generally well known. Typically, this process involves the use of a mold consisting of two separate halves or portions having cavities of particularly desired shapes and sizes. Usually, one extrudes a large-diameter, sealed tube of molten material (commonly referred to as a “parison”), places the tube between the mold halves, and closes the mold around the tube. Fluid pressure is then introduced into the tube, forcing the molten tube against the walls of the cavities, conforming the tube to the shape thereof. The pressure is maintained until the molten material cools and solidifies. The pressure is then released, the mold halves are pulled apart, and the hardened article is ejected therefrom.
One such article that is commonly manufactured in this manner is double wall cases. By producing cases in this manner, one is able to produce a device that is capable of carrying and protecting tools placed inside the case that has a multitude of desirable physical characteristics—such as rigidity, scuff resistance, and impact absorption—yet that is relatively inexpensive to manufacture. Typically, these cases will be formed using the process described above, where one mold half forms the exterior of both the base and lid portions of the case, while the other mold half forms the interior of both base and lid portions. Usually, the mold half forming the exterior of the case forms a wall with a smooth, attractive shape, while the mold half that forms the interior of the case is often molded with compartments to hold specific contents, such as, for example, a pistol-type soldering iron and various tips therefore. In fact, a particular advantage of manufacturing cases in this way is that the walls formed by the two mold halves do not need to match, as the space between these walls is filled with air.
One disadvantage of these cases, however, as that, due to their double wall nature, they tend to be both heavy and cumbersome. Accordingly, it has been suggested to cut out sections of the interior walls of the case in order to utilize the wasted volume of space between the double walls. By doing so, the case can be made smaller in light of the fact that this previously unused space is now being used to house the tool. Moreover, by removing sections of the walls, the case also decreases significantly in weight. As a result, it is also much easier to mold the design of the interior of the case, as it is no longer necessary to create deep molded compartmentation, and fewer molding rejects also result.
An example of this approach is disclosed in U.S. Pat. No. 3,317,955 to Schurman, et al., which discloses the earliest known double wall case blow-molded case, illustrating a rectangular cutout of most of the inside wall of the base portion. Another example is disclosed in U.S. Pat. No. 3,327,841 to Shurman, et al., which illustrates a partial cutout shaped to accommodate the outline of a pistol-type soldering gun. The gun is further supported by a cradle molded in the outside wall of the base portion of the case, while the space under the uncut portion of the inside base is usable for storage of an electric cord, thereby maximizing the utilization of what was previously wasted unused space.
However, one problem with removing wall sections in blow-molded cases as shown in these disclosures is that, because the blow molding process involves the use of a parison with a continuous, unbroken surface, the mold itself cannot produce any holes in the blow-molded wall other than the hole or holes through which the fluid pressure is introduced. Therefore, removing these sections typically involves an additional manufacturing step, where these wall sections are cut or burned after the blow molding process is completed and the case has been ejected from the mold. For example, cutting the inner wall was often accomplished with the use of a small circular saw blade mounted to a router and guided by a molded vertical lip surrounding the area to be cut. The router was fixed and the case was moved around the router axis by hand or by mechanical means. Round holes are often cut with hole saws, or occasionally, are burned. Cutting or burning these holes after the blow molding process is completed, however, requires additional tooling and additional manufacturing steps, entailing further difficulty, time, and expense. Moreover, the process produces unwanted sawdust or charred material around the cutout lip.
Another disadvantage of removing the wall sections after the blow molding process is complete is that the blow-molding process itself takes an unnecessarily long time. Generally, when a double wall case is blow molded using injections of fluid through one or more needles, the amount of air that can be circulated within the case is severely limited. Accordingly, the amount of heat that can be removed from the inside plastic walls is also limited, and thus, because these walls must be cooled before the part can be ejected from the mold, the blow-molded cycle is slow. Similarly, draining the blowing fluid through one or more needle orifices at the end of the blowing cycle is a relatively slow process, and because the case cannot be ejected from the mold until he internal air pressure has returned nearly to atmospheric pressure, the process is somewhat slow.
What is desired, therefore, is a blow-molded case that is double walled, but is not heavy or cumbersome. What is also desired is a case that is easy and inexpensive to manufacture. What is further desired is a blow-molded case that does not produce residual sawdust and/or charred plastic. What is also desired is a case that does not require a long blow molding cycle.